The present invention relates to read/write devices for high density magnetic recording.
Conduction of flux, such as in a magnetic head, is achieved by two mechanisms: domain wall motion and domain rotation. Domain wall motion results in flux being transmitted through a head along the walls of a domain, or domains, the flux spreading out along the domain walls as the flux seeks to return to equilibrium. However, while domain wall motion facilitates conduction of flux at low frequencies, it is a poor vehicle for conduction of flux at high frequencies. Furthermore, defects in the material in a head can be the source of Barkhausen noise as wall motion is perturbed by these defects. Such noise can result in erroneous readings of recorded data.
FIG. 1a schematically shows a pole tip region 10 of a magnetic transducer, such as a prior art thin film head, configured to achieve conduction by domain rotation when reading flux from a magnetic medium. Pole P1 is provided with central magnetic domains 12, having an axis of anisotropy (easy axis) indicated by the at rest domain state arrows 14 transverse to the longitudinal axis of the pole. Pole P1 has a total width W.sub.t, which includes the width W.sub.c of the center region and the combined width 2W.sub.x of the edge domains, such that W.sub.t =W.sub.c +2W.sub.x. It is in the center region where the desired conduction by domain rotation occurs. The probability of Barkhausen noise is inversely related to center region width W.sub.c.
FIG. 1b shows a prior art pole piece P1 having a narrow width with a criss-cross domain structure. In such arrangement, the edge domains each still have a width W.sub.x but there is no appreciable width of a center conduction section. Hence, in this case, W.sub.t =2W.sub.x.
Magnetic switching in the pole tips by the rotation mechanism is preferable to switching by domain wall motion. The advantages of switching by rotation include higher frequency response, higher efficiency and low probability of Barkhausen noise.
At rest domain configuration, in part, is controlled by inducing uniaxial anisotropy during deposition. In prior art thin film heads, both positive and negative magnetostriction (in conjunction with anisotropic stress) have been used to reinforce favorable domain configurations induced by a magnetic field during plating of the head pole pieces.
The anisotropy field (H.sub.k) of a typical thin film head may be expressed in terms of effective and intrinsic anisotropy, as follows: ##EQU1## where, d=anisotropic stress, .lambda.=magnetostriction constant, where M.sub.s =saturation magnetization. Hence, the effective anisotropy field H.sub.k can be increased by controlled application of magnetostriction and anisotropic stress as a result of the deposition process and pole geometry.